A 61-year-old man with type 2 diabetes is referred from screening with ‘maculopathy’. His vision is 6/9 in the right eye. The screening grader marked the case as clinically significant macular oedema, and the patient asks what ‘clinically significant’ actually means.
Examination Findings
Right eye: retinal thickening extending to within 500 microns of the foveal centre, with hard exudates at the edge of the thickened zone. Left eye: a few microaneurysms, flat macula. No new vessels. Vision 6/9 right, 6/6 left.
Investigations
OCT right macula confirms thickening approaching the foveal centre with small intraretinal cysts. The clinical examination with a contact lens remains the reference for the CSMO definition; OCT quantifies it.
Questions to Think About
- State the ETDRS criteria for clinically significant macular oedema.
- Why does meeting CSMO criteria change management from observation to treatment?
Diagnosis
Clinically significant macular oedema (ETDRS criteria), right eye.
Reasoning
The ETDRS defined CSMO as any of: retinal thickening at or within 500 μm of the foveal centre; hard exudates at or within 500 μm of the centre with adjacent thickening; or a zone of thickening of at least one disc area with any part within one disc diameter of the centre. Meeting any criterion means the oedema threatens central vision and the ETDRS showed laser treatment halves the risk of moderate visual loss — hence treatment rather than observation. In modern practice, centre-involving oedema is usually treated with anti-VEGF first, with laser as an adjunct; non-centre-involving CSMO may still receive focal laser. Typical management: confirm centre involvement on OCT, start the anti-VEGF or laser pathway accordingly, and address blood pressure and glycaemia. Diagnosis: clinically significant macular oedema, right eye.
Differential Diagnosis
- Clinically significant macular oedema — confirmed: thickening within 500 μm of the foveal centre meets ETDRS criteria.
- Non-clinically-significant maculopathy — ruled out: exudates and thickening are too close to the centre to be merely observed.
- Macular ischaemia — considered as a co-cause of the reduced vision; angiography is reserved if vision fails to improve with oedema treatment.
Management
Treat rather than observe: for centre-involving disease, anti-VEGF injections per local protocol with OCT-guided follow-up; focal/grid laser for non-centre-involving thickening or as adjunct. Review vision and OCT at each visit; re-treat persistent oedema. Optimise systemic control. Counsel that treatment aims first to prevent further loss, with vision gain commonest with anti-VEGF in centre-involving cases.
Key Learning Points
- CSMO is a clinical definition with three ETDRS criteria (500 μm thickening, 500 μm exudates with thickening, or one disc area of thickening within one disc diameter) — memorise them, because they are the treatment threshold.
- Centre involvement on OCT now steers therapy: centre-involving CSMO usually starts with anti-VEGF, while the CSMO label itself is what moves the eye from observation to treatment.
Red Flags
- Oedema with hard exudates directly under the fovea — chronic lipid in the centre predicts poorer visual recovery; treat promptly.
- CSMO with coexistent untreated proliferative disease — both need treatment; PRP and macular therapy are planned together.
- Pregnancy with CSMO — oedema can worsen; coordinate eye and obstetric care closely.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.